Sensored brushless DC motors are used to operate any number of devices ranging from consumer devices, such as drive systems for computer hard drives and CD/DVD players to industrial machinery such as drills and conveyer systems. In particular, sensored brushless DC motors may be coupled with a fan assembly in order to provide cooling airflow to sensitive electronic components utilized by computers or other temperature sensitive equipment.
Many applications require that motorized systems perform within certain performance limits or specifications. For example, cooling fans used in military applications must be configured so that its motor provides high reliability, has low electromagnetic interference (EMI) emissions, is able to operate at a high ambient temperature, while being able to withstand contaminated environments. While many sensored brushless DC motors are suitable for such applications, they have stringent performance specifications. Indeed, it is required that the drive circuits used to control, or otherwise operate the motor, utilize costly snubber circuits.
A snubber circuit is designed to prevent a rapid rise in voltage across the stator windings of the brushless DC motor, as current through the windings is being switched during operation of the motor. One example of a snubber circuit is a capacitor that is placed in parallel across the terminals of the switching element used to operate the motor. Due to its nature, the snubber capacitor is required to be periodically discharged of any stored energy it has collected, thus consuming the energy stored in the winding inductance.
Therefore, there is a need for a drive circuit for a sensored brushless DC motor that eliminates the need for a snubber circuit. Furthermore, there is a need for a drive circuit for a sensored brushless DC motor that reduces the voltage stress on each switch of the drive circuit. In addition, there is a need for a drive circuit for a sensored brushless DC motor that provides a path for electrical current to flow and dissipate from the primary windings until the current decays to a nominal value. Furthermore, there is a need for a drive circuit for a sensored brushless DC motor that reduces the voltage stress on each control switch to that of the voltage of the DC power supply used to operate the motor. Additionally, there is a need for a drive circuit for a sensored brushless DC motor that has reduced electromagnetic interference (EMI) emissions.